High-current bushings are used in power station transformers and are located in the current path between the generator and the primary windings of the transformer, in a generator outgoer, which is generally encapsulated and is loaded with rated currents of up to 40 kA at a comparatively low rated voltage of up to 52 kV. Because of the low dielectric load and the high thermal load, high-current bushings have a relatively short electrical conductor with a large diameter. Heat produced by electrical losses in the electrical conductor of the bushing is therefore quickly passed to its two ends, which are each in the form of an electrical connection. A first of the two electrical connections is located in the oil of the transformer, and is connected to the primary winding of the transformer. As specified by the transformer manufacturers, the first electrical connection has two contact surfaces which are aligned parallel to one another. The second electrical connection is in general located in the air-filled encapsulation of the generator outgoer, and is connected to a current-carrying conductor of the outgoer.
The rated current load capacity of the high-current bushings is determined substantially by the comparatively high temperatures which occur at the electrical connections and by the maximum permissible temperature of the insulating material used in the bushing.
An electrical conductor of the type mentioned initially is used in a transformer bushing of the GOH type, and is described in the Technical Instruction 1ZSE 2750-107 de, Rev 1, 2000-04-15, issued by ABB Power Technologies AB Components, 77180 Ludvika/Sweden. This electrical conductor contains a stiff aluminum bolt. An electrical connection and cooling elements are milled into a first end of the bolt, which is passed into the oil of the transformer, with the electrical connection having two contact surfaces which are aligned parallel to one another. The second end of the bolt is guided in air and is equipped with four drilled flat connections, which are welded to the bolt.
An electrical conductor for a high-current bushing of the RTXF type, which can be used in transformers, is described in a Company Document D 4317, issued by Micafil AG, Zürich/Switzerland. This electrical conductor is tubular and contains electrical connections which are arranged at both ends of the tube. The electrical connections are in the form of plates and are held on two end plates, which close the two ends of the tube.
Known electrical conductors contain a plurality of current-carrying parts which are connected to one another by welding or soldering. Joints are therefore located in a current path which extends between the two electrical connections, and such joints increase the electrical resistance in the current path, thereby contributing to an increase in electrical losses.